In magnetic-drive pumps, a wet-end magnetic coupler is often permanently attached to the impeller. For example, the wet-end magnetic coupler may be permanently coupled to the impeller by molding the impeller and wet-end magnetic coupler together. The wet-end magnetic coupler is attached to the impeller at the impeller's rear, creating an indivisible impeller-magnetic coupler unit. If the impeller is damaged or if an impeller with a different size is required, the entire unit must be replaced.
Some pump manufacturers have removably coupled the wet-end magnetic coupler to the impeller's rear. However, removable connections between the impeller and wet-end magnetic coupler often lack stability. The background art has connected the impeller to the wet-end magnetic coupler by threaded connections, twist-on connections, and spline connections. The threaded connection and twist-on connection may loosen during occasional reverse rotation of the impeller causing the partial or complete disengagement of the magnetic coupler and the impeller. Spline connections may loosen in response to axial forces placed upon the impeller; especially where wear rings are worn. Damage to pumps can result from the failure of the background art connections. Therefore, a need exists for an impeller assembly which stays together during normal pump operation, but allows for separation of the impeller and wet-end magnetic coupler during pump maintenance.
Centrifugal pumps may have stationary shafts or rotating shafts. In pumps with stationary shafts, the shaft is stationary with respect to the pump housing and the impeller rotates about the shaft. In pumps with rotating shafts, the shaft rotates simultaneously with the impeller. All centrifugal pumps, regardless of whether or not the shaft is stationary, require shaft supports that maintain the correct orientation of the shaft with respect to the housing and bearings.
When centrifugal pumps operate, hydraulic forces are transmitted from the impeller to the shaft. The hydraulic forces have both radial and axial components. The shaft support must have the necessary mechanical strength to prevent the shaft from being misaligned. Shaft misalignment can cause deterioration of wear rings and bearings of centrifugal pumps. Even the temporary displacement of a shaft can cause impeller damage because of a reduced radial gap between the impeller and the volute. For example, the vanes of a displaced impeller or an impeller shroud may be fractured by the pressurized fluid flow.
Radial forces are often a result of operating the pump outside of a design flow range. The volute cross sectional area is only optimized for a limited capacity range called the design flow range. If the pump deviates from the design flow range, unbalanced radial forces act on the impeller. The prior art has reduced radial forces by using double-volute configurations and using diffraction vanes that radially surround the impeller. In general, radial loads increase with increasing impeller diameter and decreasing impeller speed.
Axial forces are partially caused by the pressure difference between the suction head and the pressure head. Dynamic axial forces occur because of eddy current flows around the impeller based on the geometric relationship between the impeller and the housing.
Radial and axial forces are often characterized by low frequency vibrations being transmitted throughout the pump. When the moving impeller blade passes a stationary volute, fluid turbulence causes additional vibrations in the pump. Vibrations in the centrifugal pump can cause loosening of fasteners, failure of thrust bearings, failure of radial bearings, and breakage of shafts. Therefore, a need exists for a shaft support which can tolerate radial forces and reduce vibrations.